Chemical watermark applied on finished paper



United States Patent 3,293,062 CHEMICAL WATERMARK APPLIED ON FINISHED PAPER Bruce D. Skofronick and Frans V. E. Vaurio, Appleton, Wis., assignors, by mesne assignments, to Customark Corporation, Appleton, Wis., a corporation of Wisconsln No Drawing. Filed Apr. 5, 1963, Ser. No. 270,826 Claims. (Cl. 11738) This invention relates to a method of placing a chemical watermark in finished blank paper.

It is an expensive procedure to place watermarks in paper when done while a paper web is being formed. Obviously, a small order for watermarked paper is prohibitively expensive.

This disadvantage has been overcome by providing chemical watermarks which are applied to the finished blank papers Such a process has been set out in copending application, Serial No. 78,228, filed December 27, 1960, now US. 3,140,959.

An object of this invention is a method for making chemical watermarks which are substantially insoluble and colorless.

Another object is a method for making chemical watermarks by applying a liquid chemical composition to the surface of finished paper and then curing the composition in the paper.

Another object is a method which makes watermarked paper economically and easily available.

Another object is a method which provides great versatility in the available watermark designs which can be placed in finished paper.

Another object is a method for simply and efficiently making chemical watermarks substantially at room temperature to thereby eliminate any necessity of involved procedure steps or high temperature cures.

Another object is a method for making a watermark in finished paper with a composition containing a chemical which cures into a colorless, substantially insoluble watermark design.

Another object is a method for making watermarks with a composition having resins combined with a chemical compound which together cure to a substantially insoluble, colorless and transparent watermark design.

Another object is a finished blank paper having a watermark applied by the foregoing methods.

A chemical watermark is successful if it is substantially insoluble, it doesnt have a gloss, it is colorless, it can survive under aging, it has good ink receptivity and the like, and it does not damage the finished paper. Such a successful watermark is made by applying a generally liquid composition in the configuration of a selected design to the surface of finished paper. It has been found that hexamethoxymethylmelamine, which is supplied under the trademark Cymel 300 by the American Cyanamid Company, can be combined with other ingredients to make a composition having the foregoing desirable features. Hexamethoxymethylmelamine has the follow ing chemical structure:

CH OCHz CHOH3 i o CHaOCHz N N CH2 C a it I oHQOoHl N 01120011,,

It is surprising that hexamethoxymethylmelamine makes a successful watermark since this material is not generally considered to be a resin in the sense that crosslinking can occur. Whatever the mechanism which oc- 3,293,062 Patented Dec. 20, 1966 curs maybe, it has been found that hexamethoxymethylmelamine in combination with acid curing agents, such as alkyl and aryl sulfonic acid derivatives, does harden into a colorless, substantially insoluble watermark in finished paper.

Alkyl substituted aryl sulfonic acids may be ortho, meta and paratoluene sulfonic acid; alkyl sulfonic acids such as methane sulfonic acids and ethane sulfonic acids are also useful as well as thediand tri-alkyl substituted phenyl sulfonic acids. The 0- and p-toluene sulfonic acids are excellent curing agents. Where the curing agent is identified merely as toluene sulfonic acid in the following examplcs, it is intended to represent a mixture of about percent p-toluene sulfonic acid and about 20 percent o-toluene sulfonic acid.

The combination of hexarnethoxymethylmelamine with such curing agent may alone form a useful composition,

but it is preferred to add a colorless, organic solvent to the composition. The preferred solvents are polar solvents such as glycol ethers, ketones, and like polar solvents. A widely adaptable solvent is diethyleneglycol monomethyl ether which will conveniently be referred to as methyl Carbitol.

The concentrations of the ingredients in the compositions can be varied within liberal ranges to obtain good quality chemical watermarks. It has been found that compositions containing from about 315 percent by weight of curing agent and from about 40-60 percent by weight of solvent provide workable compositions leading to good quality chemical watermarks. It has been further found that if the amount of curing agent is increased to about 20 percent by weight a good quality chemical watermark is provided after a short period of aging, say about 515 days.

Other ingredients and resins may be added to the compositions shown here to obtain chemical watermarks having modified physical and chemical characteristics. It has, for example, been found that epoxy resins maybe added to a composition of hexamethoxymethylmelamine, curing agent and solvent to obtain excellent chemical watermarks.

The following examples are set forth to illustrate various embodiments of the invention, but such examples should not be considered as an exclusive representative and teaching of the practice of the invention.

Example I Four different compositions containing different amounts of the ingredients, by weight, were prepared as The ingredients were combined substantially at room temperature in each of the separate compositions, A small amount of each composition wasspread uniformly over a glass surface with a conventional hand roller. A handstamp, having a design of selected configuration made from rubber-like material, was pressed against the wet film and then stamped on the surface of a finished sheet of paper. Several separately stamped sheets were prepared for each of the compositions. Watermarks less than 5 days old were soluble in water, ethyl alcohol, carbon tetrachloride and acetone. Watermarks aged longer than 5 days were insoluble in all of the foregoing solvents.

Side-by-side compositions identified as A and B were prepared by varying concentrations of ingredients. The only difference was that Composition A contained hexa- 4 COH, C=O, CCl and H 0. The solvent resistance of the marks was graded as either good (G) or not good (NG). Un-aged sheets containing marks were held at room temperature for a minimum period of 24 hours and un-aged sheets containing marks were held in an methoxymethylmelamme whereas Composition B conoven at 105 degrees C. for minutes. Table 1 sets forth taincd melamine formaldehyde, a well-known curable the results.

TABLE 1 Comparison 1 2 3 Composition A B A B A B Percent by Percent by Percent by Percent by Percent by Percent by weight weight weight weight weight weight Compound 54. 4 54. 4 36. 5 36. 5 46. 3 46. 3 5. 4 5. 4 l 3. (i 3. 6 l3. 9 l3. 9 O. 2 59. 9 39. 8 39. 8 e None N one None Poor Good Fair 30 Unaged Aged Unaged Aged Unagcd G G N G G N G G G N G G. N G G G G G G G G N G G N G resin. The compositions contained the following ingredients:

Hexamethoxymethylmelamine. Melamine formaldehyde. Toluene sulfonic acid. Toluene sultonic acid.

Methyl Carbitol. Methyl Carbitol.

It is seen from the foregoing table that the compositions containing hexamethoxymethylmelamine possess the desirable features of a chemical Watermark whereas the compositions containing melamine formaldehyde do not.

Table 2 sets forth data from similar compositions which differ only in that the curing agent is paratoluene sulfonic acid rather than toluene sulfonic acid mixture. The A and B compositions are identified as follows:

Hexamethoxymethylmelamine. Para-toluene sulfonic acid. Methyl Carbitol.

Melamine formaldehyde. Para-toluene sullonic acid. Methyl Oarbitol.

In the table, the percent figures are listed to correspond with the foregoing order of ingredients.

TABLE 2 Comparison 1 3 3 Composition A B A B A B Percent by Percent by Percent by Percent by Percent by Percent by weight weight weight weight weight weight Compound 54. 4 54. 4 33. 3 33. 3 30. 7 30. 7 Curing Agent a. 5. 4 5. 4 6. 7 6. 7 9, 2 9. 2 Solvent 40. 2 40. 2 60. 0 60. 0 60. 1 60. 1 Gloss None None None None None Good Distinction Good Fair Good Poor None Poor Penetration, Seconds 15 3O 7 20 10 Aged Unaged Aged Unaged Aged Unaged Aged Unaged Aged Unaged Aged Unaged Solvent Resistance:

COH G G G G G G N G N G G G G NG G G G N G- G G N G N G G G G N G G G G G G G N G N G G G G G G G G G G G N G N G G G G G The distinction of the mark was rated as good, fair, or poor. The distinction evaluation particularly relates to the clarity of the mark.

The solvent resistance of the mark was rated against four solvents, namely, alcohol, acetone, carbon tetrachlo- Sideby-side compositions identified as A and B were prepared with varying concentrations of the ingredients. The only'diiference is that A contains hexamethoxymethylmelamine whereas B contains melamine form-aldehyde,

ride, and water, which were respectively identified as a well-known curable resin. Anepoxy resin, Dow DER.

McGraW-Hill, New York; and various US. patents,

among which may be mentioned Patent Nos. 2,712,535; 2,864,775; and 2,964,694.

The compositions containing the epoxy resins are suc- 5 cessfully used when there is present about 12-3 percent,

by weight, of curing agent, and 60-10 percent of solvent.

A variety of organic solvents may be used since it is only required that the chemical ingredients be soluble in the solvent, colorless and non-corrosive to the finished paper.

10 The solvent also has a vapor pressure at room temperature sufiiciently high to quickly evaporate so the ingredients in the composition do not unduly migrate and there- Melamine formaldehyde. Dow DER. Toluene sulfonic acid. Methyl Carbitol.

TABLE 3 The compositions contained the following Table 3 sets forth the results.

dients Hexamethoxymethylmelamine. Dow DER. Toluene sulionic acid. Methyl Oarbitol.

The chemical watermarks were evaluated and graded as in Table 2.

supplied by Dow Chemical Company, was added to each composition.

lngre nun m n m w v. mmm g m y g y g mam m m P m Goo b m Good mm. .nmmm U m ma. .3 U NN m U NNNN 6 9397 1 GM 660 m0 .m mm 61 www d w mw 224 No a m d P t l t R. M P We GG P k GGG NNN A N A G NG A NNNG 3 m a a g V. g V. g Mr M ed P m no m GGGG mm U NNGG mm U NN m U N 3 ma w MW 0 MW d MW m P m P w P g A code A Good A GGGG d d d e e e g y g V. g Wm M GG bi m Go m GGG mm. U NNGG mm U NNGG m U NNN m m ma m d m d e d P RA G P s G P m GGG A G GG A GNGG A NNNG n d d d e e e V. g y g V. g b: m GGGG t m m m mu .mmm U NNNN mm U GGGG n U NNoG e m 660 00 m we m 324 No mv w e d 6 d e w P 9 P w s P g G A GGGG A coco A GNGG new m i w m mam g m y g y g wt nan m a m on mm m w m 3m.m.m. U m. M U NNGG n.We U NAGN 000 O we MW ccc d 0 MW d MW d P mm WA. m P AA P A A. G NNN A N A GGGG A GNGG 1 d d d e e e v. w v g v. g at m GGG bt m w m m U NNNG mm U Good mu U GGGG aw W ma a a a a m P a P we P g A A GGGG A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A AA e A n A A A A A m A A A A Aw m A A A A a A A A A n m A A A m A A A m m .w. m .w A a. A m m d mm m m n n m n m R m m m nn 5 a s t m m n m w m m m m m m mm m m m m m m m v m m m an w 0 0 e 0 o 0 m 0 0 0 Me 0 C C P C C C S C C C 1P S The epoxy resins used in the previous example may be by alter the design of selected configuration. The vapor any of the reaction products of bisphenol A and epichlopressure should, however, be low enough to allow the in- Such resins are Well known and are described gredients in the composition to penetrate into the paper.

in the text Epoxy Resins by Lee and Ne-ville (1957), 75 Among useful solvents are ketones, such as methylisorohydrin.

butylketone, cyclohexane; esters, such as ethyl lactate, di-butyl phthalate, and N-butyl acetate; glycol others, such as ethyleneglycol monomethyl ether, etheneglycol dimethyl ether, diet-hyleneglycol monomethyl ether; and other solvents, such as dirnethyl formamide, dimethylsultoxide, and triacetin.

We claim:

1. A method for making a colorless, substantially insoluble Watermark in finished paper which includes the steps of applying to the surface of finished paper a composition having curable hexamethoxymethylmela'mine and a curing agent therefor which is a sulfonic acid derivative selected from the class consisting of an alkyl sulfonic acid and an aryl sulfonic acid as a curing agent, applying the composition in a configuration of a selected design, and curing the composition after application to said finished paper.

2. A method for making chemical water-marks in finished paper products which includes the steps of applying to the surface of finished paper a composition having curable hexamethoxymethylmelamine, a curing agent therefor which is a sulfonic acid derivative selected from the class consisting of an alkyl sulfonic acid and an aryl sulfonic acid, and a colorless organic polar solvent, applying said composition in the configuration of a selected design, and curing the composition in the paper after application to said finished paper, whereby a colorless, substantially insoluble chemical watermark is formed.

3. The method according to claim 2 further characterized by and including the step of evaporating the solvent after the composition has been applied in the configuration of a selected design.

4. The method according to claim 2 further characterized in that the composition is applied to the surface of the finished paper substantially at room temperature and the composition cures at substantially room temperature.

5. The method according to claim 2 further characterized by and including the step of aging the applied watermark until substantial insolubility of the chemical watermark is attained.

6. A method for making a colorless, substantially insoluble chemical watermark in finished paper which includes the steps of applyin to the surface of the paper a composition having curable hexamethoxymethylmelamine, a curing agent therefor which is at least about 3 percent by weight of an alkyl substituted phenyl sulfonic acid, and at least about 40 percent by weig-ht'of a colorless polar organic solvent, applying said composition in the configuration of a selected design, and curing the composition in the paper after application to said finished paper.

7. The method according to claim 6 further characterized by and including the step of aging the applied composition in the paper until substantial insolubility of the chemical watermark is attained.

8. A method for making a colorless, substantially insoluble chemical watermark in finished paper which includes the steps of applying to the surface of the paper a composition having heXame-thoxyrnethylmelamine, a curing agent therefor which is at least about 3 percent by weight of a toluene sulfonic acid, and at least about 40 percent by weight of diethyleneglycol monomethyl ether, applying said composition in the configuration of a selected design, and curing the composition after application to said paper.

9. A method for making a chemical watermark in finished paper which includes the steps of applying to the surface of the finished paper a'composition having hexamethoxymethylmelamine, an epoxy resin, an alkyl substituted phenyl sulfonic acid curing agent for the hexarnethoxymethylmelamine in the configuration of a selected design, and curing the composition in the paper whereby a colorless, substantially insoluble chemical watermark is formed.

10. A method according to claim 9 further characterized by and including the step of aging the applied watermark until substantial ins-olubility of the chemical watermark is attained.

References Cited by the Examiner UNITED STATES PATENTS 3,140,959 7/1964 Vau-rio WILLIAM D. MARTIN, Primary Examiner.

H. W. MYLIUS, Assistant Examiner. 

2. A METHOD FOR MAKING CHEMICAL WATERMARKS IN FINISHED PAPER PRODUCTS WHICH INCLUDES THE STEPS OF APPLYING TO THE SURFACE OF FINISHED PAPER A COMPOSITION HAVING CURABLE HEXAMETHOXYMETHYLMELAMINE, A CURING AGENT THEREFOR WHICH IS A SULFONIC ACID DERIVATIVE SELECTED FROM THE CLASS CONSISTING OF AN ALKYL SULFONIC ACID AND AN ARYL SULFONIC ACID, AND A COLORLESS ORGANIC POLAR SOLVENT, APPLYING SAID COMPOSITION IN THE CONFIGURATION OF A SELECTED DESIGN, AND CURING THE COMPOSITION IN THE PAPER AFTER APPLICATION TO SAID FINISHED PAPER, WHEREBY A COLORLESS, SUBSTANTIALLY INSOLUBLE CHEMICAL WATERMARK IS FORMED. 